A microscope having a macro-objective is known, for example, from DE 32 05 305 A1. The macro-objective is referred to therein as “survey objective”. The survey objective is intended for survey observation of large object fields at magnifications between 1× and 1.6×. It is problematic to integrate such survey objectives into conventional objective turrets which carry objectives having a usual magnification for microscopic observation. The problem resides in that the parfocal length of a survey objective or macro objective is greater than that of microscope objectives having a usual magnification. The parfocal length (also “optical-mechanical overall length”) is defined as the distance between the object plane in the specimen and the shoulder of the flange by which the objective is supported on the objective turret. The use of parfocal objectives eliminates the need for refocusing when switching between two objectives using an objective turret during microscopic observation. A typical parfocal length for objectives is 45 mm. The use of a non-parfocal macro-objective would require considerable changes to be made to the microscope settings when switching to and from survey observation. One option mentioned in the cited document for integrating a survey objective into a conventional objective turret is using an arrangement in which a so-called Bertrand lens is insertable into the tube of the microscope and axially displaceable therein, or one in which such a Bertrand lens is insertable into the microscope tube and an auxiliary lens is additionally used. However, with regard to the telecentric optical path in the object space, which is advantageous for imaging purposes, these arrangements are unfavorable.
Therefore, German document DE 32 05 305 A1 proposes a survey objective which is made of two subsystems, one of which is disposed on the objective turret such that it can be switched into the optical path of the microscope, and the other optical subsystem is disposed such that can be switched into the optical path between the objective turret and the microscope tube. In this arrangement, the parfocal length of the first-mentioned subsystem is equal to that of the other switchable objectives. Further, the second-mentioned optical subsystem may be axially displaceable to allow for adjustment to the accommodation properties of the observer's eye.
The respective transmitted light research microscope “JENA VAL” of the Jenoptik Jena GmbH company achieves a maximum object field diameter of 25 mm.
The Nikon company offers 0.5× macro objectives (“Ultra-Low Mag 0.5× Objective”) including additional optics disposed in the objective space and additional optics disposed outside of the objective space in the region of the magnification changer of the microscope.
The Applicant offered a modular system for research microscopes (“Leica DM R”) where a macro objective is integrated into an objective turret by way of additional optics disposed outside of the objective space in the region of the magnification changer.
The above-described approaches for integrating a macro objective into an objective turret carrying microscope objectives of usual magnification are designed for transmitted illumination only.
For incident illumination, one option for integrating a macro objective into an objective turret carrying microscope objectives of usual magnification (here referred to as “micro objectives”) is described in DE 10 2008 032 337 A1. Here, in order to implement an imaging and incident illumination beam path, there is proposed an objective of low magnification (here referred to as “macro objective”) including a total of three lens groups. A first lens group is disposed within the usual objective parfocal length, while a second lens group is disposed at the position of the exit pupil of the macro objective. A third lens group is disposed in the incident illumination beam path between an incident illumination tube lens and a mirror of a mirror system, said mirror directing the incident illumination beam path into the first lens group of the macro objective, and from there to the object. According to an advantageous embodiment of the macro objective proposed therein, the second and third lens groups form part of this mirror system, which is disposed downstream of the first lens group of the objective, as viewed in the direction of the imaging beam path. The second lens group, which has positive refractive power, is disposed downstream of the mirror in the imaging beam path, while the third lens group is in the aforementioned position in the incident illumination beam path. The third lens group has negative refractive power and is not involved in the actual imaging of the object into the eyepiece intermediate image plane. This lens group is only involved in the incident illumination and causes a virtual image of the incident light to be formed at the position of the second lens group where the exit pupil of the macro objective is located. Thus, the (virtual) illumination pupil is placed in the rear exit pupil of the macro objective.
Finally, U.S. Patent Application Publication No. 2009/0091822 A1 discloses a zoom microscope for fluorescence microscopy, including a zoom observation optical system and a zoom illumination optical system. However, since when the zoom microscopes proposed therein are operated in the low-magnification range, it is said that the illumination pupil is far from the objective pupil, which results in the problem of shading of the incident illumination light. In order to avoid this, it is proposed here to provide an activatable optical system which forms an image of the light source near the pupil of the objective. This optical system is disposed in the incident illumination beam path here as well.